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Critically ill patients are at very high risk of developing severe infections, with incidence rates typically about 5- to 10-fold higher than general wards. Estimates from the National Nosocomial Infections Surveillance (NNIS, now the National Healthcare Safety Network [NHSN]) system demonstrated that approximately 1.7 million nosocomial infections occurred in US hospitals in 2002. Twenty-four percent of these infections occurred in the intensive care unit (ICU), a rate of 13 per 1,000 patient days,1 while other studies have demonstrated incidence rates between 9% and 37%.2,3 Critically ill patients have numerous insults to normal host mechanisms. Skin integrity is usually compromised by peripheral and central access devices or wounds. Certain immunosuppressive medications decrease the ability of the immunologic defenses to function properly. Furthermore, other underlying medical conditions, such as diabetes, malnutrition, and renal disease, may predispose patients to infectious complications.

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Antimicrobials are consistently among one of the most important and commonly prescribed drugs, and appropriate policies for their use must exist in the ICU. The success of these drugs is dependent on many factors, and it is therefore imperative for health care providers to have a clear understanding of antimicrobial use in the critically ill patient.

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General principles of antimicrobial use in critical care should include the following46:

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  • Health care providers need to have a clear understanding that all fevers and leukocytosis are not always caused by infections. Systemic inflammatory response syndrome (SIRS) can be due to many noninfectious causes; thus, empirical antimicrobials are not always indicated.
    • Pursue diagnostic studies for both infectious and noninfectious causes until a diagnosis is reached.
  • Always attempt to arrive at a diagnosis for the syndrome encountered.
    • Clinical outcomes are improved when a diagnosis is reached and targeted therapy is provided.
  • Develop an empirical antimicrobial therapy based on differential diagnosis and predicted mortality.
    • Treat patients with sepsis with broad-spectrum antibiotics empirically.
    • Modify therapy to the most narrow-spectrum antibiotic when site and microbiology of the infection is defined.
    • Source control is essential for optimal care.
  • Appropriately dose antimicrobials to achieve adequate dosing and minimize toxicity.
    • In cases of sepsis, early and appropriate administration is essential to improve survival.
    • Modification of doses in patients with renal or hepatic dysfunction.
    • Awareness of drug interactions with other medications.
  • Define and continually address duration of antimicrobial therapy.
    • Tailor therapy based on microbiologic results and clinical response.
    • Discontinue antimicrobials if a noninfectious etiology is documented.
    • Base duration of therapy on clearly established standards.
  • Address antibiotic resistance.
    • Antimicrobial stewardship.
    • Antimicrobial resistance surveillance.

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A number of factors must be considered in choosing the appropriate antimicrobial for a given infection. These can be grouped into three major categories, namely, microbial, host, and drug factors.

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Microbial Factors

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It is important for health care professionals to have some knowledge about the identity of the infecting organism or at least make a reasonable guess of its identity on available information. ...

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